Method of deoxidizing semi-killed steel



United States Patent METHOD OF DEOXIDIZING SEMI-KILLED STEEL Willard A. Carlson, Evergreen Park, Ill., assignor to United States Steel Corporation, a corporation of New Jersey No Drawing. Application September 25, 1953, Serial No. 382,463

2 Claims. (CI. 75-58) This invention relates to improvements in the deoxidation of semi-killed steel to produce a highly homogeneous ingot structure and reduce laminations in plate rolled therefrom.

Semi-killed steel as known in the art is steel which is deoxidized just sufiiciently to prevent substantial rising in the molds as does rimming steel. Conversely the degree of deoxidation is insuflicient to cause substantial falling or shrinkage in the molds resulting in a tapering hole and pipe therein as in fully or completely killed steel. Thus semi-killed steel does not have the pipe of fully killed steel which must be cropped before rolling most products nor does it have a surface layer or rim of different analysis than the interior as do rimmed ingots.

As produced by prior practices, it does have laminations believed largely to be deoxidation products. These are relatively harmless in unwelded plate products but such laminations in the weld zone region of welded products severely reduce the strength thereof and may cause failure at stresses considerably below the yield strength of the steel.

I have discovered that laminations can be substantially eliminated by using a deoxidizing ladle addition of silicon carbide (SiC) within certain limits in conjunction with certain other deoxidizing steps and steel-making practices as hereinafter described.

A conventional grade of semi-killed steel used in making Welded plate products contains .20 to 30% carbon, .80 to 1.20% manganese, .10% maximum silicon with the balance iron and residual impurities. In producing such steel in accordance with the teachings of my invention, steel is refined, preferably in an open hearth furnace, to a carbon content of about .12 to .15 about .10 to .15% manganese and less than .01% silicon. The bath is then partially deoxidized in the furnace, which is known as blocking, by addition of an exothermic mixture of ferrosilicon and sodium nitrate containing substantially 45% silicon similar to the proprietary compound known as Silex until the boiling action ceases. The bath is simultaneously recarburized and alloyed with substantially total required amount of manganese by addition of high-carbon ferromanganese, and tapped within 5 to 8 minutes after these additions are completed. The steel is then further deoxidized in the ladle just prior to teeming so as to be substantially coincident with the teeming operation by the addition of silicon carbide used in an amount corresponding to .025 to .045% of the weight of the steel in the ladle of silicon, and manganese concentration adjusted to the desired amount, care being taken never to add more than 0.6% manganese in the ladle.

This silicon range is necessary because steel with a silicon content under .025% is insufliciently deoxidized and requires excessive mold aluminum additions and steel with a silicon content over 045% is too deoxidized to permit control of deoxidation in the mold. Thus heats not within the .025%-045% silicon range will have a poor homogeneous ingot structure and excessive laminations. Following this, the steel is teemed into ingot molds and during teeming a small amount of shot aluminum, not over substantially .07 lb. per ton of steel, is added to bring the deoxidation to a point Where the steel will rise in the molds to form a slightly convex upper surface thereon.

In the event this amount of aluminum is insufiicient to properly deoxidize the ingot, additional aluminum is added substantially immediately after teeming and stirred.

In a way of illustration of the proposed practices, important features of a heat made according to my invention are tabulated below:

TABULATION Charge: Lbs.

Steel scrap 203,200 Mold scrap 19 500 Hot met Charging started at 0. 00

Charging finished- 2. l5 Melted 7.30

Silex 7% Carbon terromauganesa.

Ladle addition:

Silicon carbide 350 Ferromanganese. 2, 900 Mold addition none Lamination No. Pieces End, Edge, percent percent 34, 517deoxidized by prior process 1.14 40, 282deoxidized in accordance with invention... 28 .18

In addition to the foregoing, rejections due to blisters during rolling were reduced from 2.5 to .8%.

While I have shown and described one specific embodiment of my invention, it will be understood that this embodiment is merely for the purpose of illustration and description and that various other forms may be devised within the scope of my invention, as defined in the appended claims.

I claim:

1. The method of reducing laminations in semi-killed steel which comprises, oxidizing a metallic charge in an open hearth furnace until its carbon content is reduced to .12 to .15 adding sufficiency of silicon bearing deoxidizer to substantially prevent gas evolution, adding substantially totality of manganese called for by compositional requirements, tapping the heat, adding to the ladle 0.025% to 0.045% silicon in the form of silicon carbide, teeming the heat and treating the metal in the molds with not more than 0.07 pound of aluminum per ton of steel.

2. In the method of claim 1, the step of limiting the manganese addition to the ladle to less than 0.6% manganese.

References Cited in the file of this patent UNITED STATES PATENTS FOREIGN PATENTS Great Britain 1904 

1. THE METHOD OF REDUCING LAMINATIONS IN SEMI-KILLED STEEL WHICH COMPRISES, OXIDIZING A METALLIC CHARGE IN AN OPEN HEARTH FURNACE UNTIL ITS CARBON CONTENT IS REDUCED TO .12 TO .15%, ADDING SUFFICIENTLY OF SILICON BEARING DEOXIDIZER TO SUBSTANTIALLY PREVENT GAS EVOLUTION, ADDING SUBSTANTIALLY TOTALITY OF MANGANESE CALLED FOR BY COMPOSITIONAL REQUIREMENTS, TAPPING THE HEAT, ADDING TO THE LADLE 0.025% TO 0.045% SILICON IN THE FORM OF SILICON CARBIDE, TEEMING THE HEAT AND TREATING THE METAL IN THE MOLDS WITH NOT MORE THAN 0.07 POUND OF ALUMINUM PER TON OF STEEL. 